Extrinsic- and intrinsic-defect creation in amorphousSiO2

We have studied the creation efficiency of various intrinsic and extrinsic defects in high-[OH] amorphous silica subjected to the ultraviolet emission from an ${\mathrm{O}}_2$ plasma or ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ γ-ray radiation. Both oxygen-vacancy- and nitrogen-related defects are observed following γ-ray irradiation or ultraviolet exposure. The wavelength range responsible for defect creation is estimated to be 200≲λ≲300 nm (4≲${\mathit{E}}_{\mathrm{photon}}$≲5.9 eV). The ultraviolet power output of the plasma estimated by comparing defect yields with those from a Hg lamp (λ=185 and 254 nm) suggests 200≲P≲900 mW ${\mathrm{cm}}^{\mathrm{-}2}$ for a plasma power density ∼300 mW ${\mathrm{cm}}^{\mathrm{-}3}$. Nonbridging oxygen-hole centers and hydrogen-related defect centers as well as methyl radical (${\mathrm{CH}}_3^{.}$) defects are observed after γ-ray irradiation but not after ultraviolet exposure. The efficiency of creation of the various defects is material dependent.